IS 451 Exam 2

What range of HTTP response codes indicate there was some sort of client error? A.100s B.400s C.500s D.200s E.300s

400s

What port does the HTTPs protocol use by default? A.443/UDP B. 80/TCP C. 8443/TCP D. 443/TCP

443/TCP

What are some properties of HTTP headers. A. Seen by proxy cache. B. Part of the document C. Seen by the browser D. Included in TCP handshake

A and C

Which of these services does TCP provide? A.Connection Oriented B. Many-to-Many Interaction C. Stream Interface D. Flow control E. Feature negotiation mechanism

A and C and D

What is a property of a directory? A.Directories are usually distributed B. Directories are typically written to more often than read C. Directories are not often replicated D. Directories are easilyl extended

A and D

Which of these services does UDP provide A. Checksum B. Stream interface C. Bandwidth guarantee D. Best effort transfer

A and D

Transport layer protocols - TCP

A connections oriented 1 to 1 connection. Stream interface and a sequence of individual bytes. Reliable transport and flow control.

Why do we have content delivery networks

A content delivery network is a network of computers that deliver content on the web. Improve Internet performance • Origin server, surrogate/edge servers • ESI (Edge-Side Includes) for dynamic delivery and assembly of web documents • Server selection strategy? • Manifest files for clients

What are Directory Services

A directory service si the collection of software, hardware, processes , policies and administrative procedures involved in making the information in your directory available to the users of your directory. Specialized database o More reads than writes o More easily extended o More widely distributed o Replicated on a higher scale o Standards-based support is important

Multimedia Networking - Delay Sensitive

A fundamental characteristic of multimedia network applications End to End delay and delay jitter Jitter is the variability of packet delays within the same packet stream

Multimedia Networking - Loss Tolerant

A fundamental characteristic of multimedia networking applilcations. They are loss tollerant, infrequent losses cause minor glitches. Antithesis of data, which are loss tolerant but delay tolerant.

Processes and Sockets

A process is a program running within a host. the socket is like a door if two processes communicate within same host that's inter-process communication. Processes within different hosts exchange MESSAGES to communicate. client process initiates communication Server process waits to be contacted P2P architectures have both processes. Processes send and receive messages from its socket. sending process shoves messages out the door. Sending process relies on transport infrastructure on other side of door which brings the message to socket at receiving process.

X.500

A standward directory service for different applications. Is implimented as a distrubuted database entries have attributes, atributes have types and value A directory is a specialized database. Client-server protocols o DUA, DSA, DAP, DSP DUA is the user, DSA is the server, DAP is the directory access protocol, which connects the clients to the server, and the DSP

Multimedia Networking - VoIP

A system that can get voice over an IP stream. Needs a minimal end-to-end delay to maintain conversational aspect. speakers audio has alternating talk spurts and silent periods. Chunk and header encapsulated into UDP or TCP segment. Fixed playout delay - Receiver attempts to playout each chunk exactly q msecs after chunk was generated. the higher q is the less lost packets, but the lower it is the better the user experience.

Forward Proxy cache

A type of cache that is located close to the client that is typically deployed by the ISP. Used to decrease bandwidth usage.

Reverse Proxy cache

Also known as a gateway proxy or web accelerator. This cache is located closer to the original web server. Deployed by the web hosting ISP. Decreases load on web server. Put several together and they form a content delivery network.

Multimedia Networking - Audio

Analog audio signal sampled at constant rate. It is compressed to remove redundancy and details people cannot perceive. Quantization results in some quality reduction. telephone: 8,000 samples/sec CD music: 44,100 samples/sec

LDAP secruity

Authentication helps ensure that the opposite party is actually who they claim to be. Authentication has three forms none, basic and SASL SASL stands for Simple Authentication and Security Layer. THis is the framwork for adding additional authentication mechanisms to connection-oriented protocols. SSL and its successor TLS are the mechanisms commonly used in SASL and LDAP. It can add things like two factor authentication. Integrity is assuring that the information that arrives is the same as what was sent Confidentiality - protection of information disclosure by means of data encryption to those who are not intended to receive it. Authorization - assures that a party is really allowed to do what they have requested to do.

As of LDAP version 3, which of these is not part of the LDAP secruity model? A.Authorization B.Authentication C.Confidentiality D.Integrity

Authorization

What components are included with a directory service? A.Web services B.Client software C.Policies governing access D.Encryption services

B and C

Which of these is true? A. RTP is used to encapsulate video of ICMP. B. The sending rate in a UDP stream is often constant C. RTSP is used to control session changes for a connection D. Error Recovery with a UDP stream is typically done over the network.

B and C

What are some reasons to use compression? A. Add Encryption B. Reduce Bandwidth C. Remove details that humans tend not to perceive D. Remove Redundancy

B and C and D

Browser cache

Best for a single user. Its a cache that is implimented in a web browser that keeps track of activity in it.

This type of cache is best for a single user. A. Proxy cache B. Shared cache C. Browser cache D. Reverse proxy cache

Browser cache

Caching - Why is it good

Caching is a temporary storage of frequently accessed data. It reduces access time/latency for clients It reduces bandwidth usage, and it reduces load on a server.

Hybrid Architecture

Combines both the peer to peer and client/server architecture. Examples: Skype uses a centralized server to find the address of a remote party and then it is directed through a client. Instant messaging: chatting is peer to peer, but the server alerted when the client comes online and finds the status of their friends.

Transport Layer Protocols - UDP

Connectionless protocol and message oriented. Unreliable meaning best effort. Many to many interaction. Does not provide connection setup, reliabliity, flow control, congestion control, timing or bandwidth guaranteee.

What describes the area of the directory managed by a common authority? A.DSA B.DAP C.DSP D.DMD

DMD

DCCP

Datagram Congestion Control Protocol Over unreliable communications

Multimedia Networking - Application Classes

Different classes have different attributes Streaming - Clients request video files from servers and pipeline reception over the network and display. You can interact with it and there may be some delay Undirectional Real-Time - Like TV and radio, its a real time broadcast of something. You cannot interact, just view/listen. Interactive Real-time: Live but can be interacted with. Like Skype or a phone call. Has more delay.

Multimedia Networking - Video

Digital video is also comopressed and quantized. Displayed at a constant rate: 24 images/sec Encoded either spatially (within the image) or temporally (difference between images)

How is each object uniquely identified in a directory? A. Common Name (CN) B.Organizational Unit (OU) C.Directory Information Tree (DIT) D.Distinguished Name (DN)

Distinguished Name (DN)

Application Layer Protocols - DHCP

Dynamic Host configuration protocol. Dynamically allocates IP addresses and configuration options to hosts on a network.

What content distribution network strategy uses servers in as many access networks as possible? A. IP anycast B. Enter Deep C. Bring Home D. Edge Side Includes

Enter Deep

Freshness and Validation

Freshness - how long the document can be used from the cache without rechecking the original server. Validation - compare the cached document to the original document once its's not fresh anymore. A validator can check the last-modfieid HTTP header or the E-tag to determine of something has changed.

Application Layer Protocols - HTTP

Hypertext Transfer protocol. Web application layer protocol. Follows a client server model - client requests and displays objects and the server sends objects based on requests •HTTP 1.0: RFC 1945 •HTTP 1.1: RFC 2068 Uses TCP. Client initiates connections by creating a socket at port 80. Server accepts. Messages is exchanged and the connection is then closed HTTP is stateless - server maintains no information about past client requests 100s error are informational 200s success 300s are redirects 400s are client errors.

LDAP operations

Lightweight directory access protocol Developed as analternative to X.500, but evolved into a complete directory service. Three operation AUTHENTICATION - OPEN a connection to an LDAP server. BIND authenticates clients to the directory server. UNBIND allows the client to signal to the directory server that it is about to close its connection. INTEROGATION - Search is used to retrieve partial or complete cpies of entries matching a given set of criteria such as search base DN. COMPARE is used to deteremine whether a particular entry has an attribute value. UPDATE - ADD new entry in the DIT. DELETE to remove an entry from the directory server. MODIFY alters the content of an existing entry in the directory.

Application Layer Protocols - Email

Made of user agents, Mail servers and SMTP User agent is used to compose, edit and read messages, shows the outgoing and incoming messages. Outlook is an example. Mail server contains incoming message for the user. Also contains the emails to be sent. Has an SMT protocol between each MIME is a multimedia extension that can help encode emails. client accesses are HTTP, (Post office Protocol) POP3 and (Internet Mail Access Protocol) IMAP

P2P architecture

No always on server and end systems directly communicate peers are intermittently connected and change IP addresses. Examples include Gnutella, Freenet and Bittorrent. Highly scalable but hard to manage.

HTTP: Persistent vs non-persistent

Non-persistent HTTP can only have one object at most sent over single TCP connection. HTTP 1.0 uses nonpersistent HTTP. Persistent HTTP - multiple objects can be send over single TCP connection. Is used by HTTP 1.1

HTML META tags

Part of the document. Used for browser caching. Most proxy coaches do not look inside the document.

HTTP: Pipelining vs non-pipelining

Pipelining can only be done with a persistent connection. non-pipelining: client issues new requests only when the previous responce has been received. one RTT for each referenced object. Pipelining: The default in HTTP 1.1. Client sends request as soon as it encounters a referenced object. As little as one RTT for all referenced objects.

Multimedia Networking - RTP and RTSP

RTP specifies a packet structure for packets carrying audio and video data - a packetization protocols. It provides payload type identification, packet sequence numbering, timestamps. RTP runs in the end systems. RTSP is a client-server application layer protocol, for users to control display rewind, fast fowards, play, pause, etc. Does not have any effect on the actual streaming rate and processing.

Interception caching

Router or switch points to the cache. This way the clients don't need to be configured to point to a cache proxy. Requests are intercepted and it is forwarded to a local caching sever.

What protocol is used to send email messages between mail servers A.IMAP B.POP3 C.SMTP D.FTP

SMTP

HTTP headers

Sent before HTML document. Seen by both browser and proxy cache.

SCTP

Stream Control Transmission Protocol

Application Layer Protocols - SSH and Telnet

Telnet was udp 23 and SSH is tcp 22

This form of encoding removes redundancies that occur between two adjacent images. A. Physical B. Spatial C. Logical D. Temporal

Temporal

What happens when freshness or validator information is not available? A. The document will not be cached. B. The document will be cached according to the browser settings. C. The document will be cached according to the E-Tag label. D. The document cannot be retrieved

The document will not be cached.

Application Layer Protocols - DNS

The map between IP addresses and name. Name to address translation, aliasing Load distribution many name servers are distributed in the database TLD servers (Top-level Domain) its the server responsible for com, org. net, edu, etc. and all top level country domains. Authoritative dns servers - Organization's DNS servers, providing authoritative hostname to IP mappings for organization's servers. Recersive query is when a DNS is checking each other server for the name, while an Iterative is when the client DNS is searching each server itself.

Client/server architecture

The term indicates which side initiates contact. The server is always on and has a perminent ip address. The server waits for client contact. server class computers and the server handles multiple clients at once The client communicates with the server and must know which server it needs to contact. it only contacts the server when needed. can terminates after interacting with the server. IP address can vary. Clients do do not directly communicate with other clients

Directory Information Tree (DIT)

The tree structure of a directory information base. All objecsts are arranged in a hierarchical tree structure. Each object has a relatively distinguished name (RDN) - simple object name that is unique within a tree level Each object is identified by its distinguished name (DN) that is quique in the directory.

Application Layer Protocols - FTP

Transfer file to/from remote host. Client/server model: client initiates transfer and server is the remote host. FTP: RFC 959 and FTP server is at port 21 data connection is port 20 Control connections are used to obtain authorization for transfers. Data connections are used to move the actual files.

Multimedia Networking - Why TCP (via HTTP) or UDP

UDP sends at a constant reate that is appropriate for the client and is typically constant. has a short delay and error recovery. does not go through firewalls. HTTP sends at the maximum possible rate. It fluctates due to congestion control. larger delay. Dash is dynamic adaptive streaming over HTTP. on the server side it divides the video into multiple chunks. On the client it requests one chunk at a time.

Forward Error Correction

Uses codes containing sufficient redundancy to prevent errors by detecting and correcting them at the receiving end without retransmission of the original message

What is Jitter? A. Variation of network hop count B. Variation of packet delay C. Total network delay of a stream D. Ping response time

Variation of packet delay

Multimedia Networking - Client Buffering

When the client has moves faster than the server can stream data, the client must buffer to allow the server to catch up.

Application Requirements - Data loss

certain aplications, like sound, can have some loss. Other apps such as file transfer or telnet cannot tollerate any loss and need to be 100% reliable.

Application Requirements - Timing

certain applications need certain timing to be effective. This is critical in time sensitive information like internet telophony and interactive games.

Application Requirements - Bandwidth

some apps, like multimedia appplications, require a minimum bandwidth to be effective, while others can make use of whatever they can get. Bandwidth is the volumne of information that can be sent at a time.

How to overcome Network and delay loss

the package can be lost or delayed too much to be played to reciever. Forward Error Correction is how this is overcome.